Research suggests that between three and six percent of individuals who are otherwise unimpaired have extreme difficulties producing and understanding spoken language. This disorder is typically labeled specific language impairment. Persons diagnosed with specific language impairment (SLI) often have accompanying reading difficulties, but not all children with reading difficulties have specific language impairment.
Current research suggests that many individuals with language learning impairments have a "temporal processing deficit" that can be demonstrated by psychoacoustic measurements of several different types. They have special problems in identifying and therefore correctly sequencing rapidly successive acoustic stimuli because those successive stimuli interfere destructively with one another. This abnormal signal reception is believed to be accounted for by abnormally long integration of acoustic information in the impaired individual's neuronal processing of the sound input stream. On the basis of these findings, procedures have been developed to assess the "temporal threshold" in impaired individuals using a stimulus sequencing task in which pairs of successively presented tonal or vowel-like stimuli were varied in their durations and interstimulus intervals. The temporal threshold is the time separation (interstimulus interval) between two stimuli that are nearby in frequency, and that interstimulus intervals. The temporal threshold is the time separation (interstimulus interval) between two stimuli that are nearby in frequency, and that are of fixed frequency, intensity and duration, at which they can be accurately sequenced by the individual. This method can and has been used as a basis for screening children and adults to identify those with acoustic reception-based language learning problems, and at risk for dyslexia (reading failure).
The abnormal temporal interferences that distinguish the language impaired child appear to underlie the "fuzzy" phonetic reception and "phonological awareness" deficits that also plague them. It has been specifically demonstrated that language impaired children cannot distinguish between specific phonemes (for example, the consonant-vowel contrasts /da/ and /ba/) when the consonant transitions are presented in a fast form, but can identify them if the consonant transition is adequately prolonged in time. This has been interpreted as occurring because in its long form, critical consonant features are represented outside of the domain of destructive interference or integration that destructively alters briefer stimuli.
Studies conducted in animal models and experiments conducted in human subjects performing visual tasks have demonstrated that the correct identification of rapidly successive inputs can be improved markedly with training. On the basis of these new experimental findings and the background perspective on the acoustic reception problems of language impaired individuals described above, a training method was invented to ameliorate the "temporal processing deficits" of language impaired and dyslexic individuals, and to facilitate complex acoustic signal and language processing in general. That training approach is the subject of U.S. Pat. No. 5,813,862, to Merzenich et al., issued Sep. 29, 1998, entitled, Method and Device for Enhancing the Recognition of Speech Among Speech-Impaired Individuals, which is expressly incorporated herein by this reference. The teachings of that patent application provide a highly effective basis for overcoming, through training, the acoustic sound stream interference problems that limit signal reception in language impaired individuals. With the dramatic "clarification" of speech input that results from such training, children have been found to perform at much higher levels at a wide variety of phonetic reception, speech/language memory, syntactic, semantic, grammatical receptive and expressive language tasks. In general, after training, their language skills are elevated to normal or nearly normal "language quotient" levels.
The particular techniques described in the above-identified patent application focus on the difficulty that SLI persons have in discriminating between a pattern of brief sounds that occur in close temporal proximity to each other. The adaptive training methods taught in that patent application ordinarily involve altering the brief sounds, by prolonging them or increasing their level (intensity), and increasing the interstimulus interval (ISI) between the sounds. These changes in the sounds and in their temporal separation makes them more intelligible to the SLI person. The training program typically involves a regimen of repeated presentation of the modified sounds in a controlled pattern to the SLI individual. The individual is asked to identify the short duration sounds. The ISI between the brief sounds is gradually decreased as the individual's ability to identify the sounds improves. These improvements in the ability of the individual to discriminate between the sounds is monitored throughout the training program. As the perceptual acuity of the person continues to improve, the ISI is decreased even further and the repetition of sounds is repeated with the new ISI. It has been found that, over the course of a training program, an SLI individual's ability to distinguish between brief sounds presented in a rapid sequence may improve significantly. Eventually, as a result of the training, the SLI person may be able to discriminate between substantially unmodified brief sounds, such as consonants, which are temporally separated by an amount typical to a normal speech rate.
While these earlier procedures for the identification and remediation of language perception problems in specific language impaired individuals generally have been highly effective, there exists a need to adopt new procedures consistent with ongoing developments in the understanding of the nature and causes of these perceptual problems. For instance, these earlier treatment methods generally do not consider the potential impact of the ordering of interfering sounds upon the ability of a SLI person to distinguish between the sounds. Additionally, for example, these prior methods do not take into account the possible effects of the spectral content of the interfering sounds upon the ability of a SLI person to differentiate between sounds presented in rapid sequence or simultaneously. Thus, there has been a need to continue to develop improved methods for the identification and treatment of language perception problems in specific language impaired (SLI) individuals based upon other elements of sound patterns such as temporal ordering of the sounds and spectral content of the sounds. The present invention meets this need.